We have measured the mass and kinetic-energy distributions for fragments from the spontaneous fission of 1.2-s ${}_{}{}^{246}{}_{}{}^{}\mathrm{Fm}$ and 38-s ${}_{}{}^{248}{}_{}{}^{}\mathrm{Fm}$. The mass distributions are highly asymmetric and the average total kinetic energies of 199±4 MeV and 198±4 MeV, respectively, are consistent with systematics for lower $Z$ actinides. Their properties are in contrast to those of ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$ and ${}_{}{}^{259}{}_{}{}^{}\mathrm{Fm}$, whose spontaneous fission results in narrowly symmetric mass distributions accompanied by unusually high total kinetic energies.

RADIOACTIVITY, FISSION ${}_{}{}^{246}{}_{}{}^{}\mathrm{Fm}$ (SF) ${}_{}{}^{248}{}_{}{}^{}\mathrm{Fm}$ (SF); measured fragment-fragment kinetic energies; total kinetic energy; deduced fragment mass distributions.

• Received 17 March 1980

DOI:https://doi.org/10.1103/PhysRevC.22.1581